WITHDRAWN: Selective spectrophotometric determination of cobalt(II) in various environmental samples with 2-(chromen-2'-onyl)-5(4''-chlorophenyl)1,3,4-oxadiazole.

The present work describes a selective, rapid and economical spectrophotometric method for the determination of cobalt(II) in various environmental samples. The method is based on the formation of pink colored complex of a stoichiometric ratio 1:2 between cobalt(II) and 2-(chromen-2'-onyl)-5-(4''-chlorophenyl)1,3,4-oxadiazole at pH 6.0+/-0.2. The absorbance of the complex was measured spectrophotometrically at 542nm. Under the optical conditions, Beer's law was obeyed over the range of 0.5-14mugml(-1). The molar absorptivity and Sandell's sensitivity were 1.348x10(4)lmol(-1)cm(-1) and 0.004115mugcm(-2), respectively. The detailed study of various interferences made the method more selective. The method was successfully applied to the determination of cobalt(II) in various environmental samples. The performance of proposed method was evaluated in terms of Student's t-test and variance ratio f-test which indicates the significance of proposed method over reported method. Recoveries obtained revealed that the proposed procedure shows good accuracy at 98% confidence level.